Data transmission system and data transmission device

ABSTRACT

A data transmission device ( 1   a ) generates and transmits a lock signal for establishing clock synchronization with data transmission devices ( 1   b - n ). The data transmission device ( 1   a ) is capable of generating a pattern 1 lock signal for giving a notice of start of communication by use of data subjected to eight-value mapping, and a pattern 2 lock signal for giving a notice of start of communication by use of data subjected to four-value mapping. One of the two types of lock signals is transmitted to each data transmission device. Determining which lock signal has been received enables each data transmission device to give a notice of data communication method prior to training.

TECHNICAL FIELD

The present invention relates to a data transmission system and, morespecifically, to a data transmission system for transmitting data in aunidirectional manner according to a predetermined protocol in a ringnetwork in which a plurality of data transmission devices are connectedso as to form a ring structure.

BACKGROUND ART

In recent years, in car navigation or when doing the Internet, e.g., ITS(Intelligent Transport Systems), or transmitting image information inspace such as the inside of a motor vehicle, high-volume and high-speedcommunication is required. A great deal of study is being made oncommunication systems for transmitting such digitized video or audiodata, or digital data such as computer data or the like. Also,introduction of a network for transmitting digital data into even spacesuch as the inside of a motor vehicle is becoming more and morewidespread. For example, this intra-vehicle network uses a ring topologyas its physical topology, and connects a plurality of nodes with thering topology to form a unidirectional ring LAN, thus aiming to achieveintegrated connection of an audio device, a navigation device, aninformation terminal device, or the like. For example, Media OrientedSystems Transport (hereinafter referred to as MOST) is used for theaforementioned ring LAN as an information communications protocol. TheMOST refers to not only the communications protocol but also a methodfor constructing a distributed system. Data on a MOST network istransmitted with a frame being a basic unit, and frames are sequentiallytransmitted between the nodes in a single direction.

Noticeably, in the case of a ring LAN provided in the inside of avehicle or the like, radiated noise may cause malfunction of anotherelectronic device disposed on a motor vehicle or the like; besides,there is a necessity to perform accurate transmission without receivingany influence of radiated noise from another device. For this reason, ina ring LAN using a conventional MOST, each node is connected by use ofan optical-fiber cable, whereby protection from noise is improved whilepreventing generation of electromagnetic waves.

Meanwhile, in some examples, electrical communication (metal) isperformed using inexpensive cables such as twisted-pair cables orcoaxial cables, while data transmission at high speed exceeding 20 Mbpsis realized with a little radiated noise and improved protection fromnoise (see, for example, International Publication Pamphlet No.02/30079).

A data transmission system in which each node is connected with aninexpensive cable as describe above is described below with reference tothe drawings. FIG. 12 is a block diagram illustrating a configuration ofdata transmission system.

The data transmission system illustrated in FIG. 12 includes datatransmission devices 100 a-n and transmission lines 300 a-n. One of thedata transmission devices 100 a-n is a master data transmission device100 a, and the others are slave data transmission devices 100 b-n. Thedata transmission devices 100 a-n are connected via the transmissionlines 300 a-n so as to form a ring structure. Data is transmittedbetween the data transmission devices 100 a-n in a direction indicatedby arrows according to a communications protocol of the MOST.

In the above-described data transmission system, data transmissionemploying digital data subjected to so-called eight-value mapping isnormally performed. The data transmission by use of digital datasubjected to eight-value mapping is a kind of multi-valued transmissionin which data transmission is performed while one or more bits of dataas a data symbol is assigned to a signal level, i.e., a datatransmission method where eight degrees of signal levels are assigned(for detailed explanation, see International Publication No.WO-02/30077). Meanwhile, in recent years, in addition to the datatransmission employing data subjected to eight-value mapping, datatransmission methods other than the data transmission employing datasubjected to eight-value mapping have begun to be proposed, e.g., datatransmission employing data subjected to four-value mapping orfive-value mapping. In accordance with the appearance of such variouskinds of data transmission methods, data transmission systems whichswitch data transmission methods depending on how they are used havebegun to be proposed. Such switching of data transmission methods isgenerally carried out according to a flow as illustrated in FIGS. 13 and14. This switching between data transmission methods is described indetail below.

First, the data transmission device 100 a serving as a master generatesa lock signal for establishing clock synchronization with another datatransmission device and transmits it to the data transmission device 100b. Receiving the lock signal, the data transmission device 100 brecovers the acquired lock signal and establishes clock synchronizationwith the data transmission device 100 a. Next, the data transmissiondevice 100 b generates a lock signal and transmits it to the datatransmission device 100 c. Thereafter, the data transmission devices 100c-n each perform the same operation as the data transmission device 100b has done. Then, a lock signal transmitted by the data transmissiondevice 100 n reaches the data transmission device 100 a. Thus, clocksynchronization is established between the data transmission devices 100a-n.

Next, the data transmission device 100 a creates a training signal forsetting determination levels, which will serve as reference for datadetermination, and transmits it to the data transmission device 100 b.The training signal transmitted at this time may be a training signalfor eight-value mapping or a training signal for another method.However, it is assumed that a training signal for eight-value mapping istransmitted here.

Receiving the training signal, the data transmission device 100 b usesthe acquired training signal to set determination levels, which willserve as reference for data determination for eight-value mapping. Next,the data transmission device 100 b creates a training signal foreight-value mapping and transmits it to the next data transmissiondevice 100 c. Thereafter, the data transmission devices 100 c-n eachperform the same operation as the data transmission device 100 b hasdone. Then, a training signal transmitted from the data transmissiondevice 100 n reaches the data transmission device 100 a. Thus, settingof determination levels serving as reference for data determination foreight-value mapping is performed on the data transmission devices 100a-n in the data transmission system.

Next, the data transmission device 100 a transmits, to the datatransmission device 100 b, a discrimination signal for notifying theother data transmission devices 100 b-n which method will be applied todata transmission, the eight-value mapping or another method.

Receiving the discrimination signal, the data transmission device 100 bdetermines, based on the received discrimination signal, which methodwill be employed for data transmission. Based on the determinationresult, the data transmission device 100 b generates a discriminationsignal and transmits it to the next data transmission device.Thereafter, the data transmission devices 100 c-n each perform the sameoperation as the data transmission device 100 b has done. Adiscrimination signal transmitted from the data transmission device 100n is received by the data transmission device 100 a. Thus, the datatransmission devices 100 a-n included in the data transmission systemrecognize the method to be employed for data transmission.

Next, the data transmission device 100 a creates a training signal forthe data transmission method recognized by the data transmission devicesand transmits it to the data transmission device 100 b. Thereafter, thedata transmission devices perform the same process as theabove-described training process. Thus, the setting of determinationlevels, which serve as reference for data determination for the datatransmission method to be employed for communication, is performed onthe data transmission devices 100 a-n. Thereafter, data communicationstarts in the data transmission system.

DISCLOSURE OF THE INVENTION

As described above, in the above-described conventional datatransmission system, a training process is performed once after asynchronization process using the lock signal, and thereafter, thedetermination levels set by the training process are used to perform aprocess for discriminating between eight-value mapping and the othermethod. Thereafter, a training process is performed again, using atraining signal for the transmission method recognized by theabove-described discrimination process, and then, data communication isstarted. That is, in the conventional data transmission system, thetraining process is required to be performed twice. This is because, inthe above-described conventional data transmission system, thediscrimination process for recognizing the data transmission methodcannot be performed before a training process is performed.

Therefore, an object of the present invention is to provide a datatransmission system in which, before a training process is performed,predetermined information to give a notice of the data transmissionmethod or the like can be presented to the data transmission devices.

In a data transmission system according to the present invention, masterlock signal generation means generates a lock signal for establishingclock synchronization with the slave data transmission devices ininitial operation of the ring network, the lock signal havingpredetermined information embedded therein; master transmission meansoutputs the lock signal generated by the master lock signal generationmeans to a slave data transmission device connected downstream thereofto relay the lock signal through the ring network; slave reception meansreceives the lock signal outputted from the master transmission means;and information acquisition means acquires the predetermined informationfrom the lock signal received by the slave reception means.

Also, the master lock signal generation means may generate a pluralityof patterns of lock signals including the predetermined information of aplurality of types; the master data transmission device may furtherinclude determination means for determining, from among the plurality ofpatterns of lock signals, which pattern of lock signal to cause themaster lock signal generation means to output; and the mastertransmission means may transmit that pattern of lock signal which thedetermination means has caused the master lock signal generation meansto output.

Also, the information acquisition means may further include storagemeans for storing signals identical to the plurality of patterns of locksignals, and may compare the lock signal received by the slave receptionmeans with the signals stored in the storage means and determine whichpattern of lock signal has been acquired, thereby acquiring thepredetermined information.

Also, the information acquisition means may further include storagemeans for storing, for each of the plurality of patterns of locksignals, a pattern of differences in signal level between each symboland a symbol positioned next to that symbol in the lock signal, anddifference means for obtaining differences in signal level between eachsymbol and a symbol positioned next to that symbol in the lock signalreceived by the slave reception means, and may compare the differencesobtained by the difference means with the patterns of differences of thelock signals stored in the storage means, and determine which pattern oflock signal has been acquired, thereby acquiring the predeterminedinformation.

Also, the slave data transmission devices each may include slave locksignal generation means for generating a lock signal having a patternidentical to the pattern of the lock signal determined by theinformation acquisition means, and slave transmission means fortransmitting the lock signal generated by the slave lock signalgeneration means to a data transmission device connected downstreamthereof.

Also, the slave data transmission devices each may further includesynchronization means for establishing clock synchronization with themaster data transmission device based on the lock signal received by theslave reception means, and the information acquisition means may acquirethe predetermined information included in the lock signal, based ontiming of the clock synchronization established by the synchronizationmeans.

Also, it is desirable that the predetermined protocol be MOST (MediaOriented Systems Transport).

Also, it is desirable that each data transmission device performcommunication by use of an electric signal.

It is desirable that a plurality of communication methods be availablein the ring network, and that the predetermined information beinformation for switching between communication methods in the ringnetwork.

Also, a multi-valued electric signal may be transmitted in the ringnetwork; a plurality of methods for setting determination levels may beavailable for determining data included in the multi-valued erectricsignal; and the communication methods in the ring network may be theplurality of methods for setting the determination levels in datacommunication.

Also, the present invention is directed not only to a system but also toa master data transmission device used in the system. Specifically, inthe master data transmission device, master clock signal creation meansgenerates a lock signal for establishing clock synchronization with theslave data transmission devices in initial operation of the ringnetwork, the lock signal having predetermined information embeddedtherein; and master transmission means outputs the lock signal generatedby the master lock signal generation means to a slave data transmissiondevice connected downstream thereof to relay the lock signal through thering network.

Also, the master lock signal generation means may generate a pluralityof patterns of lock signals including the predetermined information of aplurality of types; and the master data transmission device may furthercomprise determination means for determining, from among the pluralityof patterns of lock signals, which pattern of lock signal to cause themaster lock signal generation means to output; and the mastertransmission means may transmit that pattern of lock signal which thedetermination means has caused the master lock signal generation meansto output.

Also, it is desirable that the predetermined protocol be MOST (MediaOriented Systems Transport).

Also, it is desirable that the data be transmitted by use of an electricsignal.

Also, a plurality of communication methods may be available in the ringnetwork, and the predetermined information may be information forswitching between communication methods in the ring network.

Also, a multi-valued electric signal may be transmitted in the network;a plurality of methods for setting determination levels may be availablefor determining data included in the multi-valued erectric signal; andthe communication methods in the ring network may be the plurality ofmethods for setting the determination levels in data communication.

Also, the present invention is directed not only to the master datatransmission device but also to a slave data transmission device.Specifically, slave reception means may receive the lock signaloutputted from the master data transmission device; and informationacquisition means may acquire the predetermined information from thelock signal received by the slave reception means.

The master data transmission device may transmit one of a plurality ofpatterns of lock signals including the predetermined information of aplurality of types to be relayed through the ring network; theinformation acquisition means may further include storage means forstoring signals identical to the plurality of patterns of lock signals,and may compare the lock signal received by the slave reception meanswith the signals stored in the storage means, and determine whichpattern of lock signal has been acquired, thereby acquiring thepredetermined information.

Also, the master data transmission device may transmit one of aplurality of patterns of lock signals including the predeterminedinformation of a plurality of types to be relayed through the ringnetwork; and the information acquisition means may further includestorage means for storing, for each of the plurality of patterns of locksignals, a pattern of differences in signal level between each symboland a symbol positioned next to that symbol in the lock signal, anddifference means for obtaining differences in signal level between eachsymbol and a symbol positioned next to that symbol in the lock signalreceived by the slave reception means, and may compare the differencesobtained by the difference means with the patterns of differences of thelock signals stored in the storage means, and determine which pattern oflock signal has been acquired, thereby acquiring the predeterminedinformation.

Also, slave lock signal generation means may generate a lock signalhaving a pattern identical to the pattern of the lock signal determinedby the information acquisition means; and slave transmission means maytransmit the lock signal generated by the slave lock signal generationmeans to the master data transmission device or another of the at leastone slave data transmission device connected downstream thereof.

Also, synchronization means may establish clock synchronization with themaster data transmission device based on the lock signal received by theslave reception means, and the information acquisition means may acquirethe predetermined information included in the lock signal, based ontiming of the clock synchronization established by the synchronizationmeans.

Also, synchronization means may establish clock synchronization with themaster data transmission device based on the lock signal received by theslave reception means, and the information acquisition means mayincluded in the lock signal, based on timing of the clocksynchronization established by the synchronization means.

Also, it is desirable that the predetermined protocol be MOST (MediaOriented Systems Transport).

Also, it is desirable that the data be transmitted by use of an electricsignal.

Also, a plurality of communication methods may be available in the ringnetwork, and the predetermined information may be information forswitching between communication methods in the ring network.

Also, a multi-valued electric signal may be transmitted in the network;a plurality of methods for setting determination levels may be availablefor determining data included in the multi-valued erectric signal; andthe communication methods in the ring network may be the plurality ofmethods for setting the determination levels in data communication.

According to the present invention, the master data transmission devicetransmits a lock signal having predetermined information embeddedtherein to each slave data transmission device at the time of initialoperation. Therefore, each slave data transmission device is able toacquire the predetermined information before a training process.

Also, since a lock signal having a pattern selected from previouslyprepared patterns is transmitted, the master data transmission device isnot required to generate information within itself and generate a locksignal based on the information. This allows the master datatransmission device to have a simple internal structure. Also, sincepatterns of lock signals to be transmitted are previously determined,the slave data transmission device is able to perform determinationeasily.

Also, the slave data transmission device knows beforehand the patternsof lock signals to be transmitted, and compares the lock signal receivedafter transmission with this knowledge, thereby acquiring information.In other words, it is made possible to acquire information only bydetermining with which pattern of the lock signals the pattern of thelock signal corresponds. This allows the slave data transmission deviceto acquire the information easily and have a simple internal structure.

Also, instead of the value of each symbol being used for determination,a difference between the value of each symbol and the value of a symbolnext to the symbol is used for determination; therefore, influence offluctuation or difference of a direct-current component occurringbetween transmission and reception can be eliminated. Moreover, it ismade possible that the predetermined information is acquired by simpledetermination.

Also, instead of a lock signal outputted from the master datatransmission device circulating through the ring network, each slavedata transmission device generates a lock signal identical to a locksignal it receives. This decreases the probability that a problem ofdeterioration of a lock signal as a result of being transmitted througha long transmission line will occur.

Also, by the lock signal, the slave data transmission device is able toestablish synchronization with the master data transmission device and,in addition, acquire predetermined information.

Also, even in a data transmission system to which MOST is applied,information is embedded in a lock signal, whereby it is made possible toreport the information to each slave data transmission device.

Also, in a data transmission system for electrical communication,information is embedded in a lock signal, whereby it is made possible toreport the information to each slave data transmission device.

Also, in many cases, information as to the communication method isrequired to be reported in the initial operation stage. Embedding theinformation as to the communication method in a lock signal makes itpossible to report the information as to the communication method toeach slave data transmission device in an early stage. As a result,reduction of time for initial operation and reduction of processing loadon each data transmission device at the time of initial operation areachieved.

In general, a communication method is a method for determining levels ofdigital values of transmitted data. Such methods include, for example, acommunication method by use of data subjected to four-value mapping anda communication method by use of data subjected to eight-value mapping.Information as to these methods is commonly reported after a process ofsetting the determination levels (i.e., a training process), whichfollows a synchronization process performed with the lock signal. Then,after the report is made, a training process is performed again for thecommunication method which is reported. Thus, a training process hasbeen required to be performed twice. In contrast, according to thepresent invention, since the aforementioned information is included in alock signal, each slave data transmission device is able to know thecommunication method after the lock signal is transmitted. As a result,the need to perform a training process twice is eliminated.

Also, the master data transmission device transmits a lock signal havingpredetermined information embedded therein to each slave datatransmission device at the time of initial operation. Thus, the masterdata transmission device is able to report the predetermined informationto the slave data transmission device before a training process.

Also, since a lock signal having a pattern selected from previouslyprepared patterns is transmitted, the master data transmission device isnot required to generate information within itself and generate a locksignal based on the information. This allows the master datatransmission device to have a simple internal structure.

Also, even in a master data transmission device for MOST, information isembedded in a lock signal, whereby it is made possible to report theinformation to each slave data transmission device.

Also, in a master data transmission device for electrical communication,information is embedded in a lock signal, whereby it is made possible toreport the information to each slave data transmission device.

Also, in many cases, information as to the communication method isrequired to be reported in the initial operation stage. Embedding theinformation as to the communication method in a lock signal makes itpossible to report the information as to the communication method toeach slave data transmission device in an early stage. As a result,reduction of time for initial operation and reduction of processing loadon each data transmission device at the time of initial operation areachieved.

In general, a communication method is a method for determining levels ofdigital values of transmitted data. Such methods include, for example, acommunication method by use of data subjected to four-value mapping anda communication method by use of data subjected to eight-value mapping.Information as to these methods is commonly reported after a process ofsetting the determination levels (i.e., a training process), whichfollows a synchronization process performed with the lock signal. Then,after the report is made, a training process is performed again for thecommunication method which is reported. Thus, a training process hasbeen required to be performed twice. In contrast, according to thepresent invention, since the aforementioned information is included in alock signal, each slave data transmission device is able to know thecommunication method after the lock signal is transmitted. As a result,the need to perform a training process twice is eliminated.

Also, at the time of initial operation, a lock signal havingpredetermined information embedded therein is transmitted from themaster data transmission device to each slave data transmission device.Thus, each slave data transmission device is able to acquire thepredetermined information before a training process.

Also, the slave data transmission device knows beforehand the patternsof lock signals to be transmitted, and compares the lock signal receivedafter transmission with this knowledge, thereby acquiring information.In other words, it is made possible to acquire information only bydetermining with which pattern of the lock signals the pattern of thelock signal corresponds. This allows the slave data transmission deviceto acquire the information easily and have a simple internal structure.

Also, instead of the value of each symbol being used for determination,a difference between the value of each symbol and the value of a symbolnext to the symbol is used for determination; therefore, influence offluctuation or difference of a direct-current component occurringbetween transmission and reception can be eliminated.

Also, instead of a lock signal outputted from the master datatransmission device circulating through the ring network, each slavedata transmission device generates a lock signal identical to a locksignal it receives. This decreases the probability that a problem ofdeterioration of a lock signal as a result of being transmitted througha long transmission line will occur.

Also, by the lock signal, the slave data transmission device is able toestablish synchronization with the master data transmission device and,in addition, acquire the predetermined information.

Also, even in a slave data transmission device to which MOST is applied,it is made possible to acquire the predetermined information embedded ina lock signal.

Also, it is made possible that even a slave data transmission device forelectrical communication acquires predetermined information embedded ina lock signal.

Also, in many cases, information as to the communication method isrequired to be reported in the initial operation stage. Embedding theinformation as to the communication method in a lock signal makes itpossible to report the information as to the communication method toeach slave data transmission device in an early stage. As a result,reduction of time for initial operation and reduction of processing loadon each data transmission device at the time of initial operation areachieved.

In general, a communication method is a method for determining levels ofdigital values of transmitted data. Such methods include, for example, acommunication method by use of data subjected to four-value mapping anda communication method by use of data subjected to eight-value mapping.Information as to these methods is commonly reported after a process ofsetting the determination levels (i.e., a training process), whichfollows a synchronization process performed with the lock signal. Then,after the report is made, a training process is performed again for thecommunication method which is reported. Thus, a training process hasbeen required to be performed twice. In contrast, according to thepresent invention, since the aforementioned information is included in alock signal, each slave data transmission device is able to know thecommunication method after the lock signal is transmitted. As a result,the need to perform a training process twice is eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an overall configuration of adata transmission system according to an embodiment of the presentinvention.

FIG. 2 is a block diagram illustrating a structure of a datatransmission device according to an embodiment of the present invention.

FIG. 3 is a block diagram illustrating a detailed structure of atransmission/reception section according to an embodiment of the presentinvention.

FIG. 4 is a block diagram illustrating a detailed structure of a locksignal generation section according to an embodiment of the presentinvention.

FIG. 5 is a diagram illustrating a waveform of a “pattern 1 locksignal”.

FIG. 6 is a diagram illustrating a waveform of a “pattern 2 locksignal”.

FIG. 7 is a diagram illustrating data outputted from a differencesection and data stored in a first ROM and a second ROM.

FIG. 8 is a block diagram illustrating a detailed structure of a patterndiscrimination section.

FIG. 9 is a diagram for explaining an operation of a shift register.

FIG. 10 is a flowchart illustrating initial operations performed by amaster data transmission device and a slave data transmission devicebefore data communication is started.

FIG. 11 is a flowchart illustrating initial operations performed by themaster data transmission device and the slave data transmission devicebefore data communication is started.

FIG. 12 is a block diagram illustrating an overall configuration of aconventional data transmission system.

FIG. 13 is a diagram illustrating a flow of signals between a masterdata transmission device and slave data transmission devices in theconventional data transmission system, before data communication isstarted.

FIG. 14 is a diagram illustrating a flow of signals between the masterdata transmission device and the slave data transmission devices in theconventional data transmission system, before data communication isstarted.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention is described withreference to the drawings. FIG. 1 is a block diagram illustrating anoverall configuration of a data transmission system to which datatransmission devices according to the present embodiment are applied.

In FIG. 1, the data transmission system has a ring topology as itsphysical topology in which a plurality of nodes are connected accordingto the ring topology, thereby forming a unidirectional ring LAN. Anexample of such a data transmission system is described below where thenodes are composed of data transmission devices 1 a-n, which areconnected via transmission lines 3 a-n so as to form a ring structure,and transmitted data is transmitted via transmission lines 3 a-n in asingle direction. To the data transmission devices 1 a-n are connectedconnected-devices (e.g., audio devices, navigation devices, orinformation terminal devices) 2 a-n each performing a process based ondata transmitted through the data transmission system and outputting theresult to the data transmission system. Note that as a common hardwareconfiguration, the data transmission devices 1 a-n and theconnected-devices 2 a-n respectively have integral structures.

For example, Media Oriented Systems Transport (hereinafter referred toas MOST) is used as an information communications protocol for theabove-described data transmission system. Data transmitted using theMOST as the communications protocol is transmitted with a frame being abasic unit, and frames are sequentially transmitted between the datatransmission devices 1 in a single direction. In other words, the datatransmission device 1 a outputs data to the data transmission device 1 bvia the transmission line 3 a. The data transmission device 1 b outputsthe data to the data transmission device 1 c via the transmission line 3b. The data transmission devices 1 c-n each perform the same operationas the data transmission device 1 b has done, thereby outputting thedata to the next data transmission device. Then, the data outputted fromthe data transmission device 1 n is inputted to the data transmissiondevice 1 a. Inexpensive cables such as twisted-pair cables or coaxialcables are used as the transmission lines 3 a-n, and the datatransmission devices 1 mutually perform electrical communication(metal). At the time of turning on of power of the data transmissionsystem, the data transmission device 1 a is a master, which transmitsdata with a clock of its own, and the other data transmission devices 1b-n are slaves, which lock the frequency to the clock generated at themaster.

In the data transmission system according to the present embodiment, thedata transmission devices are capable of performing communication by useof data subjected to four-value mapping or data subjected to eight-valuemapping. At the time of initial operation performed when startingcommunication, the master data transmission device 1 a notifies each ofthe data transmission devices 1 b-n which of the following will be usedby the data transmission devices to perform communication, datasubjected to four-value mapping and data subjected to eight-valuemapping. More specifically, the data transmission device 1 a embeds, ina lock signal for establishing clock synchronization with the datatransmission devices 1 b-n, information for recognizing which of thefollowing will be used for communication, data subjected to four-valuemapping and data subjected to eight-value mapping, and transmits theinformation to the data transmission devices 1 b-n.

With reference to FIG. 2, the configuration of the data transmissiondevice 1 is described. FIG. 2 is a block diagram illustrating theconfiguration of the data transmission device 1. The data transmissiondevice 1 includes a controller 5, a transmission/reception section 10,and a microcomputer (MPU) 15. The controller 5 is, for example, composedof an LSI. A description is given below with reference to the case wherethe MOST is used as an exemplary communications protocol used in thedata transmission system.

To the controller 5 is connected the connected-device 2 which performs aprocess based on data transmitted in the data transmission system andoutputs the result to the data transmission system. As its function, thecontroller 5 converts data from the connected-device 2 connected theretointo a protocol stipulated by the MOST, and outputs digital data TX tothe transmission/reception section 10; and digital data RX outputtedfrom the transmission/reception section 10 is inputted to the controller5 and then transmitted to the connected-device 2 connected thereto. Thesignal format of the transmission lines 3 inputted to or outputted fromthe transmission/reception section 10 is either for data subjected tofour-value mapping or for data subjected to eight-value mapping, whichis set at the time of initial operation performed when the datatransmission system starts communication.

The MPU 15 controls the controller 5, the transmission/reception section10, and the aforementioned connected-device 2 based on a transmissionmode of the data transmission device 1. For example, the MPU 15 controlsa process of switching of whether the data transmission device 1 is toperform communication by use of data subjected to four-value mapping orcommunication by use of data subjected to eight-value mapping, or thelike.

The transmission/reception section 10, typically composed of an LSI,includes, as shown in FIG. 3, a training signal generation section 105,a lock signal generation section 108, a selector 110, a S/P(Serial/Parallel) conversion section 115, a mapping section 120, aselector 122, a roll off filter 125, a DAC (digital to analog converter)130, a differential driver 135, a differential receiver 140, an ADC(analog to digital converter) 145, a roll off filter 150, an inversemapping section 155, a P/S (Parallel/Serial) conversion section 160, aclock recovery section 165, a difference section 170, a magnitudedetermination section 180, a pattern discrimination section 185, and adetermination section 190. These components are classified into threegroups, i.e., a transmission group, a reception group, and adetermination group.

First, the transmission group is described. The transmission group,which includes the training signal generation section 105, the locksignal generation section 108, the selector 110, the S/P(Serial/Parallel) conversion section 115, the mapping section 120, theselector 122, the roll off filter 125, the DAC (digital to analogconverter) 130, and the differential driver 135, transmits a signal to adata transmission device connected downstream.

The lock signal generation section 108 creates a lock signal forestablishing clock synchronization between the data transmission devices1 a-n, and, as shown in FIG. 4, includes a first lock signal generationsection 255, a second lock signal generation section 260, a selector265, and a switching instruction section 270. FIG. 4 is a block diagramillustrating a detailed structure of the lock signal generation section108.

The first lock signal generation section 255 creates a “pattern 1 locksignal” as illustrated in FIG. 5. FIG. 5 is a graph illustrating awaveform of the pattern 1 lock signal. The pattern 1 lock signal is asignal used when the data transmission devices establish clocksynchronization therebetween as well as a signal for notifying the datatransmission devices that communication is performed by use of datasubjected to eight-value mapping. One period of the pattern 1 locksignal consists of eight symbols, and it is a signal in which +1 and −1alternate at each symbol. The pattern 1 lock signal is a signalsubjected to eight-value mapping.

The second lock signal generation section 260 creates a “pattern 2 locksignal”as illustrated in FIG. 6. FIG. 6 is a graph illustrating awaveform of the pattern 2 lock signal. The pattern 2 lock signal is asignal used when the data transmission devices establish clocksynchronization therebetween as well as a signal for notifying the datatransmission devices that communication is performed by use of datasubjected to four-value mapping. One period of the pattern 2 lock signalconsists of eight symbols, and it is a signal in which +1 and −1alternate at each symbol except that a fifth symbol takes +7 and a sixthsymbol takes −7. The pattern 2 lock signal is a signal subjected toeight-value mapping.

The selector 265 outputs either the pattern 1 lock signal or the pattern2 lock signal in accordance with an instruction from the switchinginstruction section 270. The switching instruction section 270determines the type of lock signal to cause the selector 265 to outputin accordance with an instruction from the MPU 15, in the case where thecorresponding device thereof is the master. In the case where thecorresponding device thereof is a slave, the switching instructionsection 270 determines the type of lock signal to cause the selector 265to output in accordance with an instruction from the determinationsection 190.

Next, the training signal generation section 105 creates a trainingsignal for causing each data transmission devices to set determinationlevels for four-value mapping or determination levels for eight-valuemapping. If the corresponding device thereof is the master, the trainingsignal generation section 105 creates, in accordance with an instructionfrom the MPU 15, a training signal for four-value mapping or eight-valuemapping, and if the corresponding device thereof is a slave, it creates,in accordance with an instruction from the determination section 190, atraining signal for four-value mapping or eight-value mapping.

The selector 110 performs switching between the digital data TXoutputted from the controller 5 and the training signal outputted fromthe training signal generation section 105. The S/P conversion section115 converts the serial digital data TX into parallel form in order toperform multi-valued transmission. In the case where the communicationsprotocol is the MOST and communication is performed by use of datasubjected to eight-value mapping, since the controller 5 outputsinformation in two-bit-per-symbol form as the digital data TX, the S/Pconversion section 115 converts the serially-inputted data into two-bitparallel data. In the case where the transmission method is datacommunication with four-value mapping, the S/P conversion section 115does not perform the above conversion.

The mapping section 120 maps the data outputted from the S/P conversionsection 115 and the training signal created by the training signalgeneration section 105 to symbols of eight or four values. Whether theyare mapped to symbols of eight values or symbols of four values isinstructed by the MPU 15 in the case where the corresponding devicethereof is the master and instructed by the determination section 190 inthe case where the corresponding device thereof is a slave.

The selector 122 outputs either the data outputted from the mappingsection 120 or the lock signal outputted from the lock signal generationsection 108. The roll off filter 125 is a waveform shaping filter forlimiting the bandwidth of an electric signal to be transmitted andcontrolling intersymbol interference. For example, an FIR filter havinga roll-off rate of 100% is used.

The DAC 130 converts the signal subjected to the bandwidth limiting bythe roll off filter 125 into an analog signal. The differential driver135 amplifies the intensity of the analog signal outputted from the DAC130, converts it into a differential signal, and sends it to thetransmission line 3. For a pair of lead wires included in thetransmission line 3, the differential driver 135 transmits the electricsignal, which is sent, to one side (a positive side) of the lead wiresin the transmission line 3, and transmits a signal whose positive andnegative are inverse to those of the electric signal to the other side(a negative side) in the transmission line 3. In this manner, theelectric signal for the positive side and the electric signal for thenegative side are transmitted, as a pair, to the transmission 3, wherebychanges in one electric signal offset changes in the other electricsignal. Thus, radiated noise from the transmission line 3 and electricalinfluence introduced from outside can be reduced.

Next, the reception group is described. The reception group, whichincludes the differential receiver 140, the ADC (analog to digitalconverter) 145, the roll off filter 150, the inverse mapping section155, the P/S (Parallel/Serial) conversion section 160, and the clockrecovery section 165, receives a signal transmitted from an upstreamdata transmission device.

The differential receiver 140 converts the differential signal inputtedfrom the transmission line 3 into a voltage signal and outputs it to theADC 145. Since, as described above, the positive side and negative sideelectric signals are transmitted as a pair to a pair of lead wiresincluded in the transmission line 3, the differential receiver 140determines the signals with reference to difference between the positiveside and the negative side, whereby protection against electricalinfluence from outside is effectively provided. Then, the ADC 145converts the voltage signal outputted from the differential receiver 140into a digital signal.

The roll off filter 50 is an FIR filter for waveform shaping forperforming noise reduction on the digital signal outputted from the ADC145, and an FIR filter with sixteen times a symbol rate is usedtherefor, for example. It realizes a roll-off characteristic preventingintersymbol interference in conjunction with the above-described rolloff filter 150 on the transmitting side. Based on the clock recovered atthe clock recovery section 165, the inverse mapping section 155 recoversthe data before being subjected to mapping at the mapping section 120 onthe transmitting side with reference to difference between a receiveddata value and a previous value. A difference process at the inversemapping section 155 is performed using as reference the determinationlevels set by the above-described training signal, and the determinationlevels are used as ideal values in difference. By this inverse mappingprocess at the inverse mapping section 155, the received signal isconverted into parallel data. The P/S conversion section 160 convertsthe parallel data determined by the inverse mapping section 155 intoserial digital data RX, and outputs it to the controller 5.

The clock recovery section 165 recovers a clock component of the signalreceived from the transmission line 3 and outputted from the ADC 145,thereby recovering a transmission line clock. The recovered clock isused as a clock for processing of the signal on the receiving side andfor a determination process by the determination group, which isdescribed below.

Next, the determination group is described. The determination group,which includes the difference section 170, the magnitude determinationsection 180, the pattern discrimination section 185, and thedetermination section 190, determine information contained in the locksignal transmitted from a data transmission device connected upstream ofthe corresponding device thereof. More specifically, the determinationgroup determines whether an incoming lock signal indicates thatcommunication will be performed by use of data subjected to four-valuemapping or that communication will be performed by use of data subjectedto eight-value mapping.

Based on the clock recovered by the clock recovery section 165, thedifference section 170 reads the value of a symbol of the digital signaloutputted from the ADC 145, calculates a difference between the value ofthe read symbol and the value of a previously-read symbol, and outputsthe absolute value of the difference to the magnitude determinationsection 180. More specifically, in the case of the pattern 1 lock signalas illustrated in FIG. 5, each symbol takes +1 or −1 in an alternatemanner; therefore, the difference section 170 outputs data asillustrated in FIG. 7A. On the other hand, in the case of the pattern 2lock signal as illustrated in FIG. 6, the following pattern is observed:+1, −1, +1, −1, +7, −7, +1, −1. Therefore, the difference section 170outputs data as illustrated in FIG. 7B.

The magnitude determination section 180 determines whether a valueoutputted from the difference section 170 is larger than a predeterminedthreshold value. More specifically, assuming that the predeterminedthreshold value is “5”, for example, if the data as illustrated in FIG.7A is inputted, the magnitude determination section 180 outputs to thepattern discrimination section 185 the inputted data as “S”, whichrepresents “smaller than the threshold value”. On the other hand, if thedata as illustrated in FIG. 7B is inputted, the magnitude determinationsection 180 outputs “S”, which represents “smaller than the thresholdvalue”, for “2”parts, and outputs “L”, which represents “larger than thethreshold value”, for “7” and “14” parts. Note that, actually, in thecase of “S”, “0” is outputted, and in the case of “L”, “1” is outputted.

The pattern discrimination section 185 determines whether the locksignal transmitted from an upstream data transmission device is thepattern 1 lock signal or the pattern 2 lock signal, and, as illustratedin FIG. 8, includes a shift register 205, a first comparison section210, a first ROM 215, a first counter 225, a second comparison section230, a second ROM 235, and a second counter 240. FIG. 8 is a blockdiagram illustrating a detailed structure of the pattern discriminationsection 185.

The shift register 205, having a predetermined number of bits of datastored therein, deletes the oldest one bit of data every time one bit ofdata is newly inputted from the magnitude determination section 180.More specifically, as illustrated in FIG. 9A, the shift register 205 iscapable of storing eight bits of data in the present embodiment. Asillustrated in FIGS. 9B and 9C, once a bit representing “S” is newlyinputted, the shift register 205 discards the oldest data, i.e., a bitrepresenting “S”. FIG. 9 is a diagram illustrating an example of anoperation of the shift register.

In the first ROM 215, data as illustrated in FIG. 7C is stored. The dataillustrated in FIG. 7C is data outputted from the difference section 170in the case where the pattern 1 lock signal has been inputted into thedifference section 170.

Every time one bit of data is inputted to the shift register 205, thefirst comparison section 210 determines whether data stored in the shiftregister 205 corresponds with the data stored in the first ROM 215. Ifthey correspond with each other, the first comparison section 210outputs, to the first counter 225, “1”, which represents correspondence.On the other hand, if they do not correspond with each other, the firstcomparison section 210 outputs, to the first counter 225, “0”, whichrepresents non-correspondence.

The first counter 225 counts the number of “1”s outputted from the firstcomparison section 210, and, if the number of counts reaches sixteen,outputs this fact to the determination section 190. Note that the numberof counts is not limited to sixteen.

In the second ROM 235, data as illustrated in FIG. 7D is stored. Thedata illustrated in FIG. 7D is data outputted from the differencesection 170 in the case where the pattern 2 lock signal has beeninputted into the difference section 170. Note that fourth and sixthdata is “X”. This suggests that these portions may be either “S” or “L”.This is because these portions cannot be properly used fordetermination, because the fourth and sixth data is “7”, as illustratedin FIG. 7B, which is a value taking “L” or “S” in a fluctuate mannerdepending on the predetermined threshold value.

Every time one bit of data is inputted to the shift register 205, thesecond comparison section 230 determines whether data stored in theshift register 205 corresponds with the data stored in the second ROM230. If they correspond with each other, the second comparison section230 outputs, to the second counter 240, “1”, which representscorrespondence. On the other hand, if they do not correspond with eachother, the second comparison section 230 outputs, to the second counter240, “0”, which represents non-correspondence.

The second counter 240 counts the number of “1”s outputted from thesecond comparison section 230, and, if the number of counts reachessixteen, outputs this fact to the determination section 190. Note thatthe number of counts is not limited to sixteen.

Based on an output result outputted from either the first counter 225 orthe second counter 240, the determination section 190 determines whetherthe inputted lock signal is the pattern 1 lock signal or the pattern 2lock signal. In other words, the determination section 190 determineswhether the communication will be performed by use of data subjected toeight-value mapping or data subjected to four-value mapping.

Here, the reason why the data as illustrated in FIG. 7A or 7B itself isnot inputted to the pattern discrimination section 185, as describedabove, is described. In the data transmission system according to thepresent embodiment, the determination process is performed before thetraining signal is transmitted to each data transmission device.Therefore, in each data transmission device, the training process hasnot been performed yet, and the setting of the data determination levelshas not been performed yet, either. Consequently, each data transmissiondevice cannot perform precise determination of a signal level of data.Thus, the data transmission device according to the present embodimentdiscriminates between the pattern 1 lock signal and the pattern 2 locksignal by performing rough determination, i.e., that of whether thesignal level of data is larger or smaller than the threshold value.

An operation of the data transmission system constructed as describedabove is described below. Processes illustrated in the presentembodiment can be implemented by software using a computer or by usinghardware circuits dedicated to these processes.

Hereinafter, the initial operation performed by each data transmissiondevice before data communication starts in the data transmission systemis described with reference to the drawings. FIGS. 10 and 11 areflowcharts illustrating initial operations performed by the master datatransmission device and the slave data transmission devices before datacommunication starts. Herein, the data transmission device 1 a is themaster, and the data transmission devices 1 b-n are slaves.

First, power of all data transmission devices 1 a-1 n connected to thedata transmission system is turned on, and thereby, power of the datatransmission system is turned on (steps S5 and S100). At this time, theMPU 15 of the master data transmission device 1 a decides by use ofwhich the data communication will be performed, data subjected tofour-value mapping or data subjected to eight-value mapping (step S10).Thereafter, under control of the MPU 15 provided in each of the datatransmission devices 1 a-1 n, the setting of each of the datatransmission devices 1 a-1 n is reset (steps S15 and S105).

Next, the master data transmission device 1 a determines whether or notthe communication method determined by the MPU 15 thereof at step S10 iscommunication by use of data subjected to four-value mapping (step S20).In the case where it is not the communication by use of data subjectedto four-value mapping, the present process proceeds to step S25. In thecase where it is the communication by use of data subjected tofour-value mapping, the present process proceeds to step S30.

In the case where communication will not be performed by use of datasubjected to four-value mapping, the master data transmission device 1 aselects the pattern 1 lock signal including information indicating thatcommunication by use of data subjected to eight-value mapping will bestarted (step S25). An operation performed within the data transmissiondevice 1 a at step S25 is described in detail.

In the case where communication will be performed by use of datasubjected to eight-value mapping, the MPU 15 reports this fact to theswitching instruction section 270 in the lock signal generation section108. In response to this, the switching instruction section 270 controlsthe selector 265 so as to output the pattern 1 lock signal outputtedfrom the first lock signal generation section 255. Thus, the pattern 1lock signal is selected.

On the other hand, in the case where communication will be performed byuse of data subjected to four-value mapping, the master datatransmission device 1 a selects the pattern 2 lock signal includinginformation indicating that communication by use of data subjected tofour-value mapping will be started (step S30). An operation performedwithin the data transmission device 1 a at step S30 is described indetail.

In the case where communication will be performed by use of datasubjected to four-value mapping, the MPU 15 reports this result to theswitching instruction section 270 in the lock signal generation section108. In response to this, the switching instruction section 270 controlsthe selector 265 so as to output the pattern 2 lock signal outputtedfrom the second lock signal generation section 260. Thus, the pattern 2lock signal is selected.

Next, the master data transmission device 1 a transmits the lock signalselected at the above-described step S25 or 30 (step S35). Morespecifically, the lock signal outputted from the selector 122 issubjected to predetermined processes between the roll off filter 125 andthe differential driver 135, and transmitted to the slave datatransmission device 1 b.

Meanwhile, after the reset is performed, the slave data transmissiondevice 1 b is waiting while conducting determination as to whether thelock signal has been received or not (step S110). In the case where thedata transmission device 1 b receives the lock signal transmitted fromthe master data transmission device 1 a, the present process proceeds tostep S115. On the other hand, if the data transmission device 1 b doesnot receive the lock signal transmitted from the master datatransmission device 1 a, the present process returns to step S110.

In the case where the lock signal is received, the determination groupof the slave data transmission device 1 b determines whether the locksignal is the pattern 1 lock signal or not (step S115). A processperformed within the slave data transmission device 1 b at step S115 isdescribed in detail below.

The lock signal transmitted from the master data transmission device 1 ais subjected to the predetermined processes in the differential receiver140 and the ADC 145 and outputted to the clock recovery section 165 andthe difference section 170. Based on the lock signal, the clock recoverysection 165 performs clock recovery. Based on the clock recoveryperformed by the clock recovery section 165, the difference section 170obtains differences in value between each symbol of the lock signal, andoutputs such data as illustrated in FIGS. 7A and 7B to the magnitudedetermination section 180.

Next, the magnitude determination section 180 determines, with respectto each data outputted from the difference section 170, whether it islarger than the predetermined threshold value or not, and outputsdetermination results to the pattern discrimination section 185. Morespecifically, in the case where the predetermined threshold value is 5,the pattern discrimination section 185 outputs determination results “S,S, S, S, S, S, S, S” for the input data of FIG. 7A and determinationresults “S, S, S, S, L, L, L, S” for the input data of FIG. 7B. Inaccordance there with, either of the above-described two types ofdetermination results is inputted to the shift register 205 in thepattern discrimination section 185 in a bit-by-bit manner.

The first comparison section 210 compares data representing the pattern1 lock signal stored in the first ROM 215 with data stored in the shiftregister 205 every time one bit of the data is inputted to the shiftregister 205, and, if they correspond with each other, outputs “1” tothe first counter 225. Similarly, the second comparison section 230compares data representing the pattern 2 lock signal stored in thesecond ROM 235 with data stored in the shift register 205 every time onebit of the data is inputted to the shift register 205, and, if theycorrespond with each other, outputs “1” to the second counter 240.

The first counter 225 counts the number of “1”s outputted from the firstcomparison section 210. The second counter 240 counts the number of “1”soutputted from the second comparison section 230. Then, when the numberof “1”s counted reaches sixteen, the counters report this result to thedetermination section 190.

Finally, the determination section 190 determines from which counter thereport has come. Here, if the report has come from the first counter225, the determination section 190 determines that the pattern 1 locksignal has been received and recognizes that communication by use ofdata subjected to eight-value mapping will be performed in the datatransmission system. On the other hand, if the report has come from thesecond counter 240, the determination section 190 determines that thepattern 2 lock signal has been received and recognizes thatcommunication by use of data subjected to four-value mapping will beperformed in the data transmission system. Then, the determinationsection 190 reports the recognition result to each component connectedthereto. Thus, the determination process of step S115 is completed.

Returning back to description of the flowchart of FIG. 10, in the casewhere the lock signal is the pattern 1 lock signal at step S115, thepresent process proceeds to step S120. On the other hand, in the casewhere the lock signal is not the pattern 1 lock signal at step S115, thepresent process proceeds to step S125.

In the case where the lock signal is the pattern 1 lock signal, the locksignal generation section 108 selects and outputs the pattern 1 locksignal (step S120). The process performed at step S120 is the same asthat of the above-described step S25 except that the instruction fromthe MPU 15 is replaced by the report from the determination section 190;therefore, description thereof is omitted.

On the other hand, in the case where the lock signal is the pattern 2lock signal, the lock signal generation section 108 selects and outputsthe pattern 2 lock signal (step S125). The process performed at stepS125 is the same as that of the above-described step S30 except that theinstruction from the MPU 15 is replaced by the report from thedetermination section 190; therefore, description thereof is omitted.

Thereafter, the lock signal outputted from the lock signal generationsection 108 is outputted from the transmission/reception section 10 ofthe slave data transmission device 1 b to the next data transmissiondevice 1 c. In the transmission/reception section 10 of each of the datatransmission devices 1 c-n, the above-described processes of steps S110to 130 are performed. Then, finally, the slave data transmission device1 n outputs the lock signal to the master data transmission device 1 a.In response to this, the master data transmission device 1 a receivesthe lock signal (step S40).

Next, the MPU 15 of the master data transmission device 1 a determineswhether the communication method is communication by use of datasubjected to four-value mapping or not (step S45). This determination ismade based on which the MPU 15 has selected at the time of power-on ofthe system, four-value mapping or eight-value mapping. In the case wherethe communication method is communication by use of data subjected tofour-value mapping, the present process proceeds to step S50. On theother hand, in the case where the communication method is notcommunication by use of data subjected to four-value mapping, thepresent process proceeds to step S55.

In the case where the communication method is communication by use ofdata subjected to four-value mapping, the MPU 15 causes the trainingsignal generation section 105 to select and output a training signal forfour-value mapping (step S50).

On the other hand, in the case where the communication method iscommunication by use of data subjected to eight-value mapping, the MPU15 causes the training signal generation section 105 to select andoutput a training signal for eight-value mapping (step S55).

The training signal outputted from the training signal generationsection 105 passes through the selector 110, is subjected topredetermined processes between the S/P conversion section 115 and thedifferential driver 135, and is transmitted to the slave datatransmission device 1 b (step S60).

Meanwhile, after the lock signal is transmitted at step S130, the slavedata transmission device 1 b is waiting while conducting determinationas to whether the training signal is received or not (step S135). Here,if the data transmission device 1 b receives the training signaltransmitted from the master data transmission device 1 a, the presentprocess proceeds to step S140. On the other hand, if the datatransmission device 1 b does not receive the training signal transmittedfrom the master data transmission device 1 a, the present processreturns to step S135.

In the case where the training signal has been received, the slave datatransmission device 1 b determines whether the communication method iscommunication by use of data subjected to four-value mapping or not(step S140). This determination is made by the training signalgeneration section 105 based on which the determination section 190 hasrecognized at the determination at step S115, communication by use ofdata subjected to four-value mapping or communication by use of datasubjected to eight-value mapping.

In the case where it is determined that the communication method iscommunication by use of data subjected to four-value mapping, the slavedata transmission device 1 b performs a mapping process forcommunication by use of data subjected to four-value mapping, byemploying the training signal received by the inverse mapping section155 (step S143). Next, the training signal generation section 105selects and outputs the training signal for four-value mapping (stepS145). A process performed at step S145 is similar to the processperformed at step S50; therefore, a detailed description thereof isomitted.

On the other hand, in the case where it is determined that thecommunication method is communication by use of data subjected toeight-value mapping, the slave data transmission device 1 b performs amapping process for communication by use of data subjected toeight-value mapping, by employing the training signal received by theinverse mapping section 155 (step S147). Next, the training signalgeneration section 105 selects and outputs the training signal foreight-value mapping (step S150). A process performed at step S150 issimilar to the process performed at step S55; therefore, a detaileddescription thereof is omitted.

The slave data transmission device 1 b transmits to the next slave datatransmission device 1 c the training signal outputted from the trainingsignal generation section 105 (step S155). A process performed at stepS155 is similar to the process performed at step S60; therefore, adetailed description thereof is omitted.

Thereafter, the transmission/reception section 10 of each of the datatransmission devices 1 c-n also performs the above-described processesof steps S135 to S155. Then, finally, the slave data transmission device1 n outputs the training signal to the master data transmission device 1a. Accordingly, the master data transmission device 1 a receives thetraining signal (step S65). Thus, the training process is completed, anddata communication is started in the data transmission system (step S70and step S160).

As described above, in the data transmission system according to thepresent embodiment, the master data transmission device transmits toeach slave data transmission device the lock signal in which apredetermined information is embedded at the time of initial operation.This enables each slave data transmission device to acquire thepredetermined information prior to training. As a result, for example,it is made possible that each slave data transmission device recognizesprior to training which of the following will be performed,communication by use of data subjected to four-value mapping orcommunication by use of data subjected to eight-value mapping. Thismakes it possible to eliminate the need to perform a training processtwice as in conventional data transmission systems, i.e., the trainingprocess is required to be performed only once.

Note that, in the present embodiment, information as to by which of thefollowing the communication is performed is embedded in the lock signal,communication by use of data subjected to four-value mapping orcommunication by use of data subjected to eight-value mapping; however,the value of the multi-valued mapping is not limited to these. Forexample, the value of the multi-valued mapping may be five.

Note that, in the present embodiment, information as to by which of thefollowing the communication is performed is embedded in the lock signal,communication by use of data subjected to four-value mapping orcommunication by use of data subjected to eight-value mapping; however,the information embedded in the lock signal is not limited to this. Theinformation embedded in the lock signal may be any information as longas it is information to be given to each slave data transmission deviceat the time of initial operation.

Note that, in the present embodiment, two types of lock signals, i.e.,the pattern 1 lock signal and the pattern 2 lock signal, are used;however, the number of types, and the waveforms, of lock signals are notlimited to these.

Note that, in the present embodiment, differences in signal levelbetween each symbol are compared as illustrated in FIG. 7 in order todiscriminate between the pattern 1 lock signal and the pattern 2 locksignal; the method for discriminating between the pattern 1 lock signaland the pattern 2 lock signal is not limited to this. More specifically,the first comparison section 210 and the second comparison section 230may discriminate between the pattern 1 lock signal and the pattern 2lock signal by comparing values of symbols of the received lock signal.In this case, the values of the symbols are stored in the first ROM 215and the second ROM 235.

INDUSTRIAL APPLICABILITY

The data transmission system according to the present invention has theeffect of being capable of presenting, to each data transmission device,predetermined information for giving a notice of a data transmissionmethod or the like before a training process is performed, and is usableas, for example, a data transmission system for transmitting data in aunidirectional manner according to a predetermined protocol in a ringnetwork in which a plurality of data transmission devices are connectedso as to form a ring structure.

1. A data transmission system for transmitting data in a unidirectionalmanner according to a predetermined protocol in a ring network in whicha plurality of data transmission devices are connected so as to form aring structure, wherein, one of the plurality of data transmissiondevices is a master data transmission device, and the others are slavedata transmission devices, the master data transmission device includes:master lock signal generation means for generating a lock signal forestablishing clock synchronization with the slave data transmissiondevices in initial operation of the ring network, wherein symbols aremapped alternately to a positive side and a negative side, and differentamplitude levels are employed in mapping in accordance with a pluralityof communication modes prepared; and master transmission means foroutputting the lock signal generated by the master lock signalgeneration means to a slave data transmission device connecteddownstream thereof to relay the lock signal through the ring network,and the slave data transmission devices each include: slave receptionmeans for receiving the lock signal outputted from the mastertransmission means; and information acquisition means for acquiring thepredetermined information from the lock signal received by the slavereception means.
 2. The data transmission system according to claim 1,wherein, the master lock signal generation means generates a pluralityof patterns of lock signals including the predetermined information of aplurality of types, the master data transmission device further includesdetermination means for determining, from among the plurality ofpatterns of lock signals, which pattern of lock signal to cause themaster lock signal generation means to output, and the mastertransmission means transmits that pattern of lock signal which thedetermination means has caused the master lock signal generation meansto output.
 3. The data transmission system according to claim 2,wherein, the information acquisition means further includes storagemeans for storing signals identical to the plurality of patterns of locksignals, and the information acquisition means compares the lock signalreceived by the slave reception means with the signals stored in thestorage means, and determines which pattern of lock signal has beenacquired, thereby acquiring the predetermined information.
 4. The datatransmission system according to claim 2, wherein, the informationacquisition means further includes: storage means for storing, for eachof the plurality of patterns of lock signals, a pattern of differencesin signal level between each symbol and a symbol positioned next to thatsymbol in the lock signal; and difference means for obtainingdifferences in signal level between each symbol and a symbol positionednext to that symbol in the lock signal received by the slave receptionmeans, and the information acquisition means compares the differencesobtained by the difference means with the patterns of differences of thelock signals stored in the storage means, and determines which patternof lock signal has been acquired, thereby acquiring the predeterminedinformation.
 5. The data transmission system according to claim 3,wherein the slave data transmission devices each include: slave locksignal generation means for generating a lock signal having a patternidentical to the pattern of the lock signal determined by theinformation acquisition means; and slave transmission means fortransmitting the lock signal generated by the slave lock signalgeneration means to a data transmission device connected downstreamthereof.
 6. The data transmission system according to claim 1, wherein,the slave data transmission devices each further include synchronizationmeans for establishing clock synchronization with the master datatransmission device based on the lock signal received by the slavereception means, and the information acquisition means acquires thepredetermined information included in the lock signal, based on timingof the clock synchronization established by the synchronization means.7. The data transmission system according to claim 1, wherein thepredetermined protocol is MOST (Media Oriented Systems Transport). 8.The data transmission system according to claim 7, wherein each datatransmission device performs communication by use of an electric signal.9. The data transmission system according to claim 1, wherein, aplurality of communication methods are available in the ring network,and the predetermined information is information for switching betweencommunication methods in the ring network.
 10. The data transmissionsystem according to claim 9, wherein, a multi-valued electric signal istransmitted in the ring network, a plurality of methods for settingdetermination levels are available for determining data included in themulti-valued electric signal, and the communication methods in the ringnetwork are the plurality of methods for setting the determinationlevels in data communication.
 11. A master data transmission deviceconnected to at least one slave data transmission device so as to form aring structure to form a ring network, the master data transmissiondevice transmitting data in a unidirectional manner in the ring networkaccording to a predetermined protocol, the master data transmissiondevice comprising: master lock signal generation means for generating alock signal for establishing clock synchronization with the slave datatransmission devices in initial operation of the ring network, whereinsymbols are mapped alternately to a positive side and a negative side,and different amplitude levels are employed in mapping in accordancewith a plurality of communication modes prepared; and mastertransmission means for outputting the lock signal generated by themaster lock signal generation means to one of the at least one slavedata transmission device connected downstream thereof to relay the locksignal through the ring network.
 12. The master data transmission deviceaccording to claim 11, wherein, the master lock signal generation meansgenerates a plurality of patterns of lock signals including thepredetermined information of a plurality of types, the master datatransmission device further comprises determination means fordetermining, from among the plurality of patterns of lock signals, whichpattern of lock signal to cause the master lock signal generation meansto output, and the master transmission means transmits that pattern oflock signal which the determination means has caused the master locksignal generation means to output.
 13. The master data transmissiondevice according to claim 11, wherein the predetermined protocol is MOST(Media Oriented Systems Transport).
 14. The master data transmissiondevice according to claim 13, wherein the data is transmitted by use ofan electric signal.
 15. The master data transmission device according toclaim 11, wherein, a plurality of communication methods are available inthe ring network, and the predetermined information is information forswitching between communication methods in the ring network.
 16. Themaster data transmission device according to claim 15, wherein, amulti-valued electric signal is transmitted in the ring network, aplurality of methods for setting determination levels are available fordetermining data included in the multi-valued electric signal, and thecommunication methods in the ring network are the plurality of methodsfor setting the determination levels in data communication.
 17. A slavedata transmission device connected to a master data transmission deviceso as to form a ring structure to form a ring network, the ring networkincluding at least one slave data transmission device, the slave datatransmission device transmitting data in a unidirectional manner in thering network according to a predetermined protocol, wherein, the masterdata transmission device outputs a lock signal for establishing clocksynchronization in the ring network to one of the at least one slavedata transmission device connected downstream thereof to relay the locksignal through the ring network, in which, in the lock signal, symbolsare mapped alternately to a positive side and a negative side, anddifferent amplitude levels are employed in mapping in accordance with aplurality of communication modes prepared, and the slave datatransmission device comprises: slave reception means for receiving thelock signal outputted from the master data transmission device; andinformation acquisition means for acquiring the predeterminedinformation from the lock signal received by the slave reception means.18. The slave data transmission device according to claim 17, wherein,the master data transmission device transmits one of a plurality ofpatterns of lock signals including the predetermined information of aplurality of types to be relayed through the ring network, theinformation acquisition means further includes storage means for storingsignals identical to the plurality of patterns of lock signals, and theinformation acquisition means compares the lock signal received by theslave reception means with the signals stored in the storage means, anddetermines which pattern of lock signal has been acquired, therebyacquiring the predetermined information.
 19. The slave data transmissiondevice according to claim 17, wherein, the master data transmissiondevice transmits one of a plurality of patterns of lock signalsincluding the predetermined information of a plurality of types to berelayed through the ring network, the information acquisition meansfurther includes: storage means for storing, for each of the pluralityof patterns of lock signals, a pattern of differences in signal levelbetween each symbol and a symbol positioned next to that symbol in thelock signal; and difference means for obtaining differences in signallevel between each symbol and a symbol positioned next to that symbol inthe lock signal received by the slave reception means, and theinformation acquisition means compares the differences obtained by thedifference means with the patterns of differences of the lock signalsstored in the storage means, and determines which pattern of lock signalhas been acquired, thereby acquiring the predetermined information. 20.The slave data transmission device according to claim 18, comprising:slave lock signal generation means for generating a lock signal having apattern identical to the pattern of the lock signal determined by theinformation acquisition means; and slave transmission means fortransmitting the lock signal generated by the slave lock signalgeneration means to the master data transmission device or another ofthe at least one slave data transmission device connected downstreamthereof.
 21. The slave data transmission device according to claim 17,further comprising synchronization means for establishing clocksynchronization with the master data transmission device based on thelock signal received by the slave reception means, wherein theinformation acquisition means acquires the predetermined informationincluded in the lock signal, based on timing of the clocksynchronization established by the synchronization means.
 22. The slavedata transmission device according to claim 17, wherein thepredetermined protocol is MOST (Media Oriented Systems Transport). 23.The slave data transmission device according to claim 22, wherein thedata is transmitted by use of an electric signal.
 24. The slave datatransmission device according to claim 17, wherein, a plurality ofcommunication methods are available in the ring network, and thepredetermined information is information for switching betweencommunication methods in the ring network.
 25. The slave datatransmission device according to claim 24, wherein, a multi-valuedelectric signal is transmitted in the ring network, a plurality ofmethods for setting determination levels are available for determiningdata included in the multi-valued electric signal, and the communicationmethods in the ring network are the plurality of methods for setting thedetermination levels in data communication.